This invention relates to a device and method for removing anode butts from anode rods.
The electrolytic reduction of alumina to aluminium takes place in large flat vessels or cells, lined with carbon blocks on the bottom and sides. The carbon blocks in the bottom act as a cathode. The anode consists of carbon bodies, often called anode blocks, fixed to steel rods of various designs. These are called anode rods and are fixed to the live bus over the electrolytic reduction cell by means of clamps or screw fixtures. The anode rods serve a double purpose, i.e., they hold the anode blocks in the required position and conduct the electricity for the electrolytic process from the bus bar to the carbon blocks. The electrolyte consists of molten fluorides to which alumina has been added.
The electrolytic process liberates gases on the underside of the anode blocks, and these are thus oxidized and consumed.
It is thus necessary at intervals of about three weeks to remove the anode blocks and replace them with new ones.
Anode changing is performed by removing the anode rod from the anode bus and taking it away together with the remaining unconsumed carbon, called the anode butt. These remnants must be removed to prepare the rod for the fitting of a new anode block.
The present invention relates to a method and an arrangement for this operation, in the following called an anode butt remover.
The anode blocks are usually in the form of a parallelepiped,the largest face of which lying horizontal and acting as the active electrode surface. In the opposite surface there is a hole for fixing the anode rod. Usually there are two or three such holes in which the so-called studs are cast by means of molten iron, or tamped into position with a special tamping paste.
The studs are in line and are fixed at their upper ends to a steel piece, called a yoke. To this yoke there is welded a vertical aluminium rod which is the anode rod proper.
Methods practised hitherto for removing the butts have involved crushing, breaking or splitting the butts. Pulling the butts off the studs has also been tried, the rod being suspended in a suitable device. This method exposes the entire structure to large forces.
In Swedish patent document for public inspection (utlaggningsskrift) No. 384 004 an apparatus is described for stripping anode butts from studs. The butts are pressed down off the studs by haudraulic cylinders acting against clamps, which are clamped onto the extension of the anode rod, i.e., the "anode spade."The hydraulic cylinders for the clamps must act against some fixture which is not a part of the structure and thus must be provided separately.
The present invention aims at pressing the carbon remnants off the studs without these press forces being transferred to structural components other than the rod, and the rod itself is to a large extend protected from such forces.